1. Field of the Invention
The present invention relates to a method for removing a patient support such as a head support from a radiation image, e.g. from a CT image.
2. Description of the Related Art
In many medical imaging applications the patient or at least the body part that is examined is held in place by a so called table or support, supports of specific shapes are used to position and hold specific parts of the body such as a head supporting cradle or a foot or hand restraint. These supports may have different shapes and may have different positions during examination.
In the context of the preferred embodiments of the present invention table, support, restraint cradle are used as synonyms.
When a radiation image such as a CT or a CTA image, of the patient or of the body part is then taken, the final image comprises an image of the support in addition to the image of the patient or the body part.
The image of the support is sometimes removed from the image within the modality, but most of the image reconstructions still include an image of the support.
Removing support images from such images is important for several reasons, some of which are set out below.
Regarding the visualization, tables can affect the image sharpness making the diagnosis more complex. FIG. 1 shows a CT volume without and with table removal.
For patient follow up applications, images (2D images or 3D volumes) of the same patient which are taken at different periods of time are registered and compared to each other in order to follow pathology evolution. For such registration process, it is important that the image content is the same and the presence of different tables may affect the registration. In the same way, removing tables is important for PET/CT registration.
Due to the wide variability in table designs, shapes, luminosities and textures, as is shown in FIG. 2, on one hand and the inconstant patient positions on the other hand, automating the table removal process is a challenging task.
The article ‘Automatic Patient Table Removal in CT images’ by Yang-Ming Zhu et al., Journal of Digital Imaging (2012) 25:480-485 relates to automatic table removal in CT images.
The article describes a method for automatic table removal which first identifies and locates the patient table in the sagittal planes of the CT images and then removes it from the axial planes.
The method is based on thresholding with a single, fixed threshold value. The method fails when the table cross section varies axially (such as in the case of a patient head support).
It is an aspect of the present invention to provide a method for removal of an image of a support of an object from data representing a radiation image of said object, more specifically for providing a method for table removal in CT images. It is a purpose to provide such a method that is generic and automated, and that does not require any pre-acquired template representation of said support.